Process for the synthesis of phenol and acetone

ABSTRACT

This invention refers to a process for the synthesis of phenol and acetone starting from cumene hydroperoxide, and to a plant specifically developed for performing this process. More in particular, this invention refers to a process for the synthesis of phenol and acetone starting from cumene hydroperoxide, comprising the following steps: a) Pretreating of the starting cumene hydroperoxide with acidic resins, to obtain cumene hydroperoxide free of inorganic cations; b) Decomposing of the cumene hydroperoxide free of inorganic cations originating from the step (a) in the presence of acidic resins, to yield phenol and acetone.

FIELD OF THE INVENTION

This invention refers to a process for the synthesis of phenol andacetone starting from cumene hydroperoxide.

BACKGROUND ART

As known, the most widely employed industrial process for the synthesisof phenol is that providing for the decomposition of cumenehydroperoxide. At this time, over 90% of the phenol produced in theworld is synthesized by this route, which simultaneously yields a moleof acetone per mole of phenol produced in accordance with the followingreaction:C₆H₅—C(Me)₂—OOH→C₆H₅—OH+MeCOMe

The cumene hydroperoxide is prepared by oxidizing cumene with air in aliquid phase:C₆H₅—C(Me)₂+O₂→C₆H₅—C(Me)₂—OOH

The main byproducts of this reaction are acetophenone,dimethylphenylcarbinol and formic acid.

The latter in particular has, because of its acidity, the capability ofcatalyzing a partial decomposition of the cumene hydroperoxide tophenol, which even if present in parts per million, blocks the furtheroxidation of cumene with the result that the reaction is interrupted atan unacceptably low percentage of conversion.

It is known that in order to neutralize the formic acid byproductaqueous solutions of sodium salts with organic acids are introduced intothe cumene mixture so as to buffer the reaction environment. Analternative employed for the same purpose was that of using the sodiumsalt of the same cumene hydroperoxide under anhydrous conditions (U.S.Pat. No. 3,171,860 in the name of F. Codignola). On the other hand, theprocess in current use provides for feeding the oxidation reactor withcumene and caustic soda in a concentrated aqueous solution, so as tomaintain a pH of an adequately high level to prevent initiating thedecomposition of the hydroperoxide.

All the processes of the known art have in common that they utilizebases with inorganic cations (typically sodium, potassium and ammonium).Despite the fact that the reaction mixture exiting the oxidation step iswashed with water to remove the salts, the cumene hydroperoxide thusproduced still contains a small yet uneliminable percentage of inorganiccations in addition to a residual percentage of water. The presence ofsuch cations is particularly disadvantageous for performing thesubsequent decomposing reaction to yield phenol and acetone, as itinterferes with the functionality of the acidic resins which couldeffectively be employed as decomposing catalysts. This consideration haslimited the choice of acidic catalysts to traditional inorganic acids,in particular to sulphuric acid. The strong inorganic acids such assulfuric acid, however, involve considerable safety problems in usageand waste disposal condition.

SUMMARY OF THE INVENTION

The problem underlying this invention is therefore making available aprocess for the synthesis of phenol and acetone which does not providefor the application of acidic catalysts which are complex and hazardousto use.

This problem is solved by a process for the synthesis of phenol andacetone as outlined in the attached claims.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention provides for the decomposition of cumenehydroperoxide in the presence of acidic resins as decomposing catalysts,in accordance with the following reaction:

This process comprises the following two steps:

-   -   a) Pretreating of the initial cumene hydroperoxide (CHP) with        acidic resins, to obtain cumene hydroperoxide free of inorganic        cations;    -   b) Decomposing of the cumene hydroperoxide free of inorganic        cations originating from the phase (a) in the presence of acidic        resins, to yield phenol and acetone.

The step (a) of pretreating CHP with the acidic resins is preferablyperformed at such a temperature as not to cause a substantialdecomposition of CHP. More preferably, the step (a) will be performed ata temperature below 20° C. Operating under these conditions avoids theneed for setting up devices for dissipating heat at the pretreatingreactor, which are otherwise needed because of the exothermal nature ofthe decomposing reaction.

The step (b) of decomposing the cumene hydroperoxide is exothermic andproceeds rapidly to a CHP conversion of about 100%. The temperatureduring this phase is maintained between 35° C. and 90° C., preferablybetween 40° and 50° C.

The acidic resin will preferably be employed, both in the CHPpretreating step (a) and in the decomposing step (b), in quantitiescomprised between 2% and 25%, preferably between 5% and 15% by weightwith respect to the hourly flow rate of CHP in each of the pretreatingand decomposing reactors, respectively. The quantity of acidic resinwill more preferably be about 10% by weight with respect to the hourlyflow rate of CHP.

The acidic resin used in the process of this invention will preferablybe chosen from ion exchange resins having sulphonic acid (—SO₃H)functional groups linked to an organic chain, preferably a polystyreneor styrene-divinylbenzene polymer. Preferred acidic resins are chosenfrom the group Amberlyst™ 15, Amberlyst™ 18 and Nafion™. The latter inparticular is a sulphonic resin with a perfluoridated chain,characterized by high stability to elevated temperatures.

The process of the invention preferably comprises a step (c) of drawingup a portion of the reaction mixture exiting the step (b), a step (d) ofcooling said portion of the reaction mixture to a temperature of 35-45°C., more preferably of about 40° C., and a step (e) of recirculating thesame to the decomposing reactor. This makes it possible to dilute thecumene hydroperoxide entering the decomposing step (b) with the alreadyreacted product, so as to limit the temperature increase due to theexothermal nature of the reaction. The quantity of product recycled inaccordance with the steps (c), (d) and (e) will be comprised between 80%and 95% by weight, preferably about 90% by weight, of the reactionmixture exiting the step (b).

The process of the invention may also comprise a step of regeneratingthe acidic resin employed in said CHP pretreating step (a). Said acidicresin regenerating step will preferably be performed by treating with asolution of sulphuric acid, for instance with sulphuric acid at 15% byweight. More preferably, the resin may first be washed with water andacetone. Provision may also be made for washing with water aftertreating with the sulphuric acid solution.

A plant specifically developed for implementing the process of theinvention constitutes a further object of this invention.

Such a plant will comprise a CHP decomposing reactor containing apreestablished quantity of acidic resin and set up upstream of such adecomposing reactor, at least one reactor for pretreating the cumenehydroperoxide with said acidic resins. Preferably, at least two reactorswill be provided for pretreating CHP with acidic resin, where said atleast two pretreating reactors are set up in parallel and operating inan alternating manner. This will in fact make it possible to perform theregeneration of the acidic resin contained in one of the two or morepretreating reactors without a need for interrupting the process. Twopretreating reactors set up in parallel will generally be adequate toensure the continuity of the process, while in principle not excluding aprovision for three or more pretreating reactors. In the above mentionedcase of two preatreating reactors, the CHP feeding line will split upinto two parallel paths, each passing through a preatreating reactor,which may be mutually excluded.

Downstream of the decomposing reactor, provision will be made for aproduct discharging line, from which a line will preferably be providedfor recirculating the reaction mixture so as to return it the CHPdecomposing reactor after crossing the appropriate heat exchangingmeans. In case a provision is made for such a recirculation of thereaction mixture, the volume of each of the pretreating reactors will beless than the volume of the decomposing reactor by a factor generallyproportional to the ratio between the flow rate of the recirculatedfluid and the flow rate of the feeding fluid.

The invention will now be further described by an example of anembodiment, as outlined below for indicative and non-limiting purposes,with reference to the following figures:

FIG. 1 shows a simplified block diagram of a plant for implementing theprocess of this invention.

The cumene hydroperoxide is fed along a line A which splits up into twoparallel lines A1, A2 each leading to a pretreating reactor 1 a, 1 b forthe cumene hydroperoxide. Appropriate flow regulating means V1, V2, forinstance valve units, allow selecting the operating line, andconsequently the reactor 1 a or 1 b associated with the same, whileexcluding the other line.

The pretreating reactors 1 a, 1 b will be equipped with cooling means,for instance a cooling jacket 2 a, 2 b, and in the reactors the acidicresin will be introduced in a predetermined amount depending on thehourly rate expected in the plant.

The respective tranferring lines B1, B2 for the pretreated cumenehydroperoxide will be derived from said preatreating reactors 1 a, 1 b,so as to join up in a single charging line B leading to the cumenehydroperoxide decomposing reactor 3. Appropriate pumping means P willtake care of moving the fluid mass between the reactors.

The decomposing reactor 3 contain the acidic resin in the appropriateamount and is also equipped with cooling means, in the example with acooling jacket 4.

A discharge line C conveys the reaction products of the decomposingreactor 3 to a product isolating section set up at a downstream location(not shown). From said discharge line C a line D is derived forrecirculating a portion of the reaction mixture, which after crossing aheat exchanger 5, returns the reaction mixture to the pumping means Pand from there to the charging line B of the decomposing reactor 3.

The acidic resin used in the pretreating reactors and in the decomposingreactor may be the same, or alternatively different resins may beemployed. For instance, it will be possible to use Amberlyst™ 15 or 18in the pretreating reactors and Nafion™ in the decomposing reactor,where the exothermal nature of the reaction may advise the usage of ahigh temperature resistant resin.

A particular example of an embodiment of the process of the inventionwill now be described for purely indicative purposes.

EXAMPLE

This example describes a process implemented in a plant like that shownin FIG. 1.

Cumene hydroperoxide (CHP) having a purity of 93% and containing 16.4 mgof sodium cation per kg of CHP are introduced, at a flow rate of 6tons/hour, into a pretreating catalyst 1 a containing 600 kg ofAmberlyst™ 18 ion exchange resin. This reactor is kept at a temperaturebelow 20° C. by a cooling jacket.

The CHP exiting the pretreating reactor 1 a is analyzed by atomicabsorption, which detects no further trace of a sodium cation. This CHPis then conveyed along the line B into a decomposing reactor 3containing 6 tons of Amberlist™ 18, after having been mixed with 54tons/hour of decomposition products recirculated at a temperature ofabout 40° C., as specified below.

The decomposing reactor 3 is appropriately cooled by a cooling jacket 4,so that the reaction products exiting the reactor have a temperature ofabout 42° C., despite the exothermic nature of the reaction which maycause the temperature within the reactor to locally build up to 50° C.or more.

These reaction products are discharged, at a flow rate of 60 tons/hour,from the reactor 3 and conveyed toward the recovery unit. A substantialportion of the same, amounting to 54 tons/hour, is instead drawn up,cooled to about 40° C. in a heat exchanging unit 5 and then recirculatedto the decomposing reactor, after mixing with fresh CHP (6 tons/hour).The portion of reaction products exiting the reactor at a flow rate of 6tons/hours is analyzed, evidencing a CHP conversion matching thetheoretical value.

The advantages of the process of this invention are evident from theforegoing description.

In essence, the use of the acidic resin in the CHP pretreating stepallows eliminating the inorganic cations fom the CHP, thus making itpossible to perform the decomposing step of the same to yield phenol andacetone by using the acidic resin and therefore under moderateconditions and without generating any residues difficult to dispose of.

The CHP, pretreated as described above to eliminate the inorganiccations, does not cause a saturation of the resin's acidic sites due tosaid cations in the decomposing reactor. This reactor can thereforeoperate on a continuous basis, without requiring a regeneration of theresin.

The provision for at least two CHP pretreating reactors allows tooperate the process in a continuous manner, stopping one forregenerating the resin while operating the other.

It is evident that only certain particular embodiments of the process ofproducing phenol and acetone as an object of this invention have beendescribed, which the expert will be capable of providing with all thosemodifications needed for its adaptation to particular and contingentrequirements, without thereby deviating from the scope of protection ofthis invention.

1. A process for the synthesis of phenol and acetone starting fromcumene hydroperoxide, comprising the following steps: a) pretreating thestarting cumene hydroperoxide with acidic resins, to obtain cumenehydroperoxide free of inorganic cations; b) decomposing the cumenehydroperoxide free of inorganic cations originating from the step (a) inthe presence of acidic resins, to yield phenol and acetone.
 2. A processaccording to claim 1, wherein said step a) of pretreating cumenehydroperoxide with the acidic resins is performed at a temperature suchas not causing a substantial decomposition of CHP.
 3. A processaccording to claim 1, wherein said step a) of pretreating the cumenehydroperoxide with the acidic resins is performed at a temperature below20° C.
 4. A process according to claim 1, wherein said step b) ofdecomposing the cumene hydroperoxide is performed at a temperaturecomprised between 35° C. and 90° C., preferably between 40° C. and 50°C.
 5. A process according to claim 1, wherein said acidic resin isemployed both in the step (a) of pretreating as in the step (b) ofdecomposing the cumene hydroperoxide, in amounts comprised between 2%and 25% by weight with respect to the hourly flow rate of cumenehydroperoxide in each of the steps (a) of pretreating and (b) ofdecomposing, respectively.
 6. A process according to claim 5, whereinsaid acidic resin is employed both in the step (a) of pretreating as inthe step (b) of decomposing the cumene hydroperoxide, in amountscomprised between 5% and 15% by weight with respect to the hourly flowrate of cumene hydroperoxide in each of the steps (a) of pretreating and(b) of decomposing, respectively.
 7. A process according to claim 6,wherein the amount of acidic resin is about 10% by weight with, respectto the hourly flow rate of cumene hydroperoxide.
 8. A process accordingto claim 1, wherein said acidic resin is chosen among ion exchangeresins having sulphonic acid functional groups (—SO₃H) tied to anorganic chain, preferably to a polystyrene or styrene-divinylbenzenepolymer.
 9. A process according to claim 8, wherein said acidic resin ischosen from the group Amberlyst™ 15, Amberlyst™ 18 and Nafion™.
 10. Aprocess according to claim 1, further comprising a step (c) of drawing aportion of the reaction mixture exiting the decomposing step (b) of thecumene hydroperoxide, a step (d) of cooling said portion of the reactionmixture at a temperature of 35° C. to 45° C., more preferably of about40° C., and a step (e) of recirculating the same to the decomposing step(b).
 11. A process according to claim 10, wherein the amount of productrecycled according to steps (c), (d) and (e) is comprised between 80%and 95% by weight, preferably about 90% by weight of the reactionmixture exiting from the decomposing step (b).
 12. A process accordingto claim 1, further comprising a regenerating step for the acidic resinused in said step (a) of pretreating the cumene hydroperoxide.
 13. Aprocess according to claim 12, wherein said acidic resin regeneratingstep is performed by treating with a solution of sulphuric acid,preferably a sulphuric acid at 15% by weight.
 14. A plant for performingthe process as outlined in claim 1, comprising: a decomposing reactor(3) of the cumene hydroperoxide, containing a pre-established amount ofacidic resin; at least one preatreatment reactor (1 a, 1 b) of thecumene hydroperoxide with said acidic resins, where said at least onepretreating reactor is set up upstream of said decomposing reactor (3);recirculating means (D, P) of a portion of the products of thedecomposing reaction to said decomposing reactor (3); optionally, heatexchanging means (5) set up downstream of said decomposing reactor (3)along the recirculating line of said portion of products of thedecomposing reaction, optionally, cooling means of said decomposingreactor (3) and of said at least one pretreating reactor (1 a, 1 b). 15.A plant according to claim 14, comprising at least two pretreatingreactors (1 a, 1 b) of cumene hydroperoxide with acidic resin, wheresaid at least two pretreating reactors are set up in parallel andoperating in an alternating manner.